Friction compensation for vehicle system control

Abstract

A computer includes a processor and a memory storing instructions executable by the processor to determine a planned curvature of a planned path of a vehicle, determine a friction-compensation torque based on image data received from a camera of the vehicle, and control a steering system of the vehicle based at least in part on the planned curvature and the friction-compensation torque. The friction-compensation torque compensates for friction internal to the steering system.

What is claimed is: 
     
       1. A computer comprising a processor and a memory storing instructions executable by the processor to:
 determine a planned curvature of a planned path of a vehicle based at least in part on image data received from a camera of the vehicle; 
 determine a planned velocity of a component of a steering system of the vehicle based on the planned curvature; 
 determine a friction-compensation torque based on the image data and at least in part on the planned velocity, the friction-compensation torque compensating for friction internal to the steering system; and 
 control the steering system based at least in part on the planned curvature and the friction-compensation torque. 
 
     
     
       2. The computer of  claim 1 , wherein the instructions further include instructions to determine an uncompensated torque based on the planned curvature, and controlling the steering system is based at least in part on the uncompensated torque. 
     
     
       3. The computer of  claim 2 , wherein controlling the steering system includes actuating a steering motor of the steering system to apply a total torque equal to a sum of the uncompensated torque and the friction-compensation torque. 
     
     
       4. The computer of  claim 2 , wherein determining the uncompensated torque includes minimizing an error between the planned curvature and an actual curvature. 
     
     
       5. The computer of  claim 1 , wherein determining the friction-compensation torque includes applying a low-pass filter to a function returning a sign of the planned velocity, and the sign of the planned velocity represents a direction of motion of the component of the steering system. 
     
     
       6. The computer of  claim 5 , wherein the low-pass filter has a gain equal to a Coulomb friction of the steering system. 
     
     
       7. The computer of  claim 6 , wherein the Coulomb friction of the steering system is based on a speed of the vehicle. 
     
     
       8. The computer of  claim 5 , wherein the low-pass filter has a time constant equal to a ratio of a relaxation-length parameter of the steering system and an absolute value of the planned velocity. 
     
     
       9. The computer of  claim 8 , wherein the relaxation-length parameter is a ratio of a Coulomb friction of the steering system and a stiffness coefficient of the steering system. 
     
     
       10. The computer of  claim 9 , wherein the relaxation-length parameter is based on a speed of the vehicle. 
     
     
       11. The computer of  claim 1 , wherein the planned velocity of the component is proportional to a derivative of the planned curvature with respect to time. 
     
     
       12. The computer of  claim 1 , wherein the planned velocity of the component is an angular velocity. 
     
     
       13. The computer of  claim 1 , wherein the instructions further include instructions to determine a road model based on the image data, the road model is a polynomial equation that predicts points on a center line of a lane of travel of the vehicle, and determining the planned curvature is based on the road model. 
     
     
       14. The computer of  claim 1 , wherein determining the friction-compensation torque based on the image data is feedforward. 
     
     
       15. The computer of  claim 1 , wherein determining the friction-compensation torque includes calculating the friction-compensation torque using a Dahl friction model. 
     
     
       16. The computer of  claim 1 , wherein controlling the steering system includes performing centering of the vehicle within a lane. 
     
     
       17. The computer of  claim 16 , wherein the instructions further include instructions to detect boundaries of the lane in the image data. 
     
     
       18. A method comprising:
 determining a planned curvature of a planned path of a vehicle based at least in part on image data received from a camera of the vehicle; 
 determining a planned velocity of a component of a steering system of the vehicle based on the planned curvature; 
 determining a friction-compensation torque based on the image data and at least in part on the planned velocity, the friction-compensation torque compensating for friction internal to the steering system; and 
 controlling the steering system based at least in part on the planned curvature and the friction-compensation torque.